Characterization of the unidirectional corrosion of oilwell cement exposed to H₂S under high-sulfur gas reservoir conditions

Abstract

A dense gypsum layer was formed on the surface of gas-exposed sample.The corrosion of H 2 S on oilwell cement is considered to be a great challenge for wellbore integrity and environmental safety in the exploitation of high-sulfur gas reservoir. In this paper, the corrosion performances of oilwell cement exposed to humid H 2 S gas and H 2 S-rich brine were investigated using designed unidirectional samples. Compressive strength, microhardness, porosity, gas permeability, SEM, EDS, and XRD analyses were conducted to compare the dissimilarity of H 2 S attack in two exposure scenarios. The experimental results show that the corrosion degree of cement exposed to humid H 2 S gas was lower due to a dense gypsum layer formed on the cement surface; this layer inhibited inward penetration of H 2 S by blocking diffusion. On the contrary, a porous and loose amorphous silica gel section formed on the headspace of brine-exposed cement for dissolution and migration effects of brine, which facilitated the penetration of H 2 S to the interior of cement. The degradation mechanism of cement and the effects of exposure scenario on cement properties are proposed. This journal is © The Royal Society of Chemistry [year] [journal], [year], [vol], 00-00 | 5 Fig. 7 SEM images and EDS elemental spectra of gas-exposed sample.

Application of a new reduced‐complexity assessment tool to estimate CO2 and brine leakage from reservoir and above‐zone monitoring interval (AZMI) through an abandoned well under geologic carbon storage conditions

“…Such wells can potentially compromise the integrity of caprock layers that would otherwise prevent unwanted vertical fluid migration out of the storage system and into receptors of concern (i.e., potable groundwater formations and the atmosphere) . Degradation of the abandoned wells prior to or during their contact with injected CO 2 may also create pathways for CO 2 and brine to leak upward along the well: between the cement sheath and formation rock, through the cement sheath, between the cement sheath and the casing, through the cylindrical space within the casing if the casing is corroded, and through cement plugs if they are damaged or degraded …”

Experimental Investigation of CO2‐ and Fe3O4‐Assisted Corrosion at the Cement–Casing Interface

“…[ 2 ] Corrosive substances could reach the surface of the casing steel along the cracks or defected areas of the cement ring, which will cause the casing steel to perforate or even be directly scrapped, leading to huge economic losses. [ 3,4 ]…”

“…[2] Corrosive substances could reach the surface of the casing steel along the cracks or defected areas of the cement ring, which will cause the casing steel to perforate or even be directly scrapped, leading to huge economic losses. [3,4] The exploitation of oil and gas resources is developing toward deep and ultradeep wells recently due to the lack of gas and oil resources. [5] With increasing the borehole depth, complex formations with high-pressures will appear and stabilization of the high pressure is required by effective cementing.…”

Identification of potential CO2 leakage pathways and mechanisms in oil reservoirs using fault tree analysis

“…As for the injection and production wells, the long‐term production activities can lower the strength of casing tubing and cement, producing small cracks, by which CO 2 can flow out of the wellbore into the surrounding surface soils before it goes deep into the bottom hole. Besides, CO 2 is a weak corrosive gas, and it can corrode casing tubing and cement, further lowering the strength of the casing tubing and cement, generating more cracks 23–27 . Once CO 2 leaks out and seeps into the atmosphere and ground water, it can cause health, safety, and environmental disasters 28–30 .…”